Selichos (for Ashkenazim) begin this Motzaei Shabbos, September 28th.
Selichos are generally recited each morning before davening, although some say it the night before (after chatzos, according to many).
One should say Birchas Hatorah each morning before reciting Selichos.
Selichos, especially the Yud Gimmel Middos (Hashem, Hashem…), should be said with concentration and sincerity.
It is more worthwhile to daven at one's own pace than to rush through to keep up with the minyan. However, when the congregation reaches the Yud Gimmel Middos, one should say it along with them.
When the congregation reaches Tachanun, one should say Tachanun and the congregation need not return to make up for what he skipped.
Someone saying Selichos without a minyan omits the Yud Gimmel Middos and the Aramaic passages following Tachanun (Machei Umasei, etc.).
There is a minhag for the Sheliach Tzibbur of Selichos to serve as the Sheliach Tzibbur for the other Tefillos that day.